1) Field of the Invention
The present invention relates to improvements on motors, and more particularly to improvements on stator casings of motors.
2) Related Art
FIG. 4 shows a conventional stepping motor. The stepping motor has a stator 51 that is formed from a coil bobbin 61 and a coil bobbin 62 disposed adjacent to one another in the axial direction. A coil 61a is wound around the coil bobbin 61 and a coil 62a is wound around the coil bobbin 62. An inner yoke 55 equipped with pole teeth 55a and an inner yoke 56 equipped with pole teeth 56a are disposed adjacent to one another between the coil bobbins 61 and 62. An outer yoke 57 equipped with pole teeth 57a and an outer yoke 58 equipped with pole teeth 58a are disposed outside in the axial direction of the coil bobbins 61 and 62. The outer yoke 57 is formed in a manner to cover the exterior side of the coil 61a, and the outer yoke 58 is formed in a manner to cover the exterior side of the coil 62a, such that the outer yokes 57 and 58 respectively serve as an exterior casing of the motor. A rotor 52 having a rotor shaft 53 is disposed within an internal peripheral surface of the stator 51 opposite to the pole teeth 55a -58a. A cap 54 is attached to one end face of the stator 51. A bearing 54a is disposed in the cap 54 such that the bearing 54a supports one end of the rotor shaft 53.
FIG. 5 shows an exterior view of the stepping motor. Opening sections 57b and 58b are provided in the external yokes 57 and 58 that serve as the motor casing, respectively. The terminal section 63 protrudes from a window section that is formed by the opening sections 57b and 58b. The terminal section 63 has terminal pins 63a, 63c, 63b and 63d fixedly provided at equal intervals thereon. The terminal pin 63a is connected to a winding start section of the winding 61a, the terminal pin 63c is connected to a winding end section of the winding 61a, the terminal pin 63b is connected to a winding start section of the winding 62a and the terminal pin 63d is connected to a winding end section of the winding 62a. 
The motor thus constructed in a manner described above has a structure in which, as shown in FIG. 6, one end of the rotor shaft is supported by a frame. A channel shaped frame 65 is affixed to a stator 51.
As described above, one end of the rotor shaft 53 of the rotor 52 is supported by a bearing that is formed in the cap 54 on one side of the stator 51, and the other end of the rotor shaft 53 passes through the stator 51 and protrudes to a great extent on the other side. In other words, the rotor shaft 53 of the rotor 52 passes through a passing aperture 71a that is formed in a plane section 71 of the frame 65 that is affixed to the stator 51, and one end of the rotor shaft 53 is supported on a bearing 73 that is mounted on a plane section 72 of the frame 65 that opposes to the plane section 71. An external peripheral surface of a section of the rotary shaft 53 that protrudes on the side of the frame 65 defines a lead screw section 67.
The motor having the structure described above is assembled in the following manner. First, the frame 65 is affixed to one end surface of the stator 51. Then, as shown in FIG. 7, one end of the rotor shaft 53 of the rotor 52 is inserted in the stator 51 on the side where the frame 65 is not mounted (in a direction indicated by the arrow in FIG. 7). When the end of the rotor shaft 53 passes the internal surface of the stator 51 and the passing aperture 71a of the frame 65 and reaches the bearing 73 (see FIG. 6) that is mounted on the frame 65, the cap 54 is attached to the stator 51. In this manner, the motor is assembled.
In the motor having the structure described above, an exterior casing that encloses the exterior of the stator 51 is formed from external peripheral sections of the external yoke 57 equipped with the pole teeth 57a and the external yoke 58 equipped with the pole teeth 58a. The external casing has a relatively complex configuration, and is composed of two members that are divided up and down in the axial direction. In addition, connecting sections between the external yokes 57 and 58 are provided with the opening sections 57b and 58b, respectively. Therefore, when the external yokes 57 and 58 are disposed adjacent to each other in the axial direction, the opening sections 57b and 58b need to be carefully aligned with each other. Accordingly, a mold for making the external casing has a complex configuration, and the assembly efficiency is poor.
Also, in the above-described motor, when one end of the rotor shaft 53 of the rotor 52 is passed through the internal empty space within the stator 51 and protruded on the side of the frame 65, and is supported by the bearing 73 that is mounted on the frame 65, there is a risk that the lead screw section 67 collides with an internal surface of the passing aperture 71a that is formed in the plane section 71 of the frame 65. In other words, when the works described above are performed, the rotor shaft 53 needs to be maintained perpendicular to the plane section 71, and the center of the rotor shaft 53 needs to coincide with the center of the passing aperture 71a. These tasks are very difficult. Moreover, there is only a small difference between the diameter of the passing aperture 71a formed in the plane section 71 that serves as an affixing surface of the frame 65 to be affixed to the stator 51 and an external diameter of the lead screw 67. In addition, since the passing aperture 71a is punched out by a press machine, edges of the aperture may have burrs. Therefore, unless the works are carefully conducted, the rotor shaft 53 could be inserted with its center being eccentric with respect to the passing aperture 71a, as shown in FIG. 7. As a result, the lead screw section 67 may come in contact with the internal surface of the passing aperture 71a and scrape the burrs, which may clog the male screw of the lead screw 67 or damage the male screw of the lead screw section 67. As a result, when the male screw of the lead screw section 67 is damaged, noise may be generated due to the damage in the lead screw section 67 when the motor is driven. When the male screw of the lead screw section 67 is clogged with burrs, noise may likewise be generated or the motor may become inoperable during its operation.
It is an object of the present invention to provide a motor that can be readily manufactured and readily assembled with respect to a stator of the motor by simplifying the structure of an exterior casing of the motor.
It is another object of the present invention to provide a motor that can prevent damages on a lead screw section of a rotary shaft when the rotor is assembled, and also prevent generation of metal powder from burrs at a passing aperture of a frame or the lead screw section that may be scraped when the rotor is assembled.
In accordance with an embodiment of the present invention, a motor has a stator including a coil bobbin with winding sections to be wound by windings and a terminal section that outwardly protrudes in a radial direction of the coil bobbin and has fixed protruded terminal pins that are to be connected to winding start sections and wiring end sections of the windings. In one aspect of the embodiment of the present invention, a curled case covers an exterior of the windings of the stator. The curled case may preferably be formed by curling a flat metal plate along a peripheral direction of the stator. The curled case has end sections in the peripheral direction and an opening section defined by the end sections of the curled case. The terminal section protrudes through the opening section, and the opening section may preferably open at an opening arc angle defined by less than one half of the entire periphery of a circle (i.e., less than 180 degrees). Since an exterior casing of the motor is formed from the curled case, the exterior casing can be readily manufactured and readily assembled. Also, since the opening section of the curled case is formed to be less than one half of the entire periphery of a circle (i.e., less than 180 degrees), the curled case is readily retained by, for example, external peripheral sections of the yokes when it is placed over the stator. The curled case can be readily affixed to the yokes by, for example, welding or the like.
In accordance with one embodiment of the present invention, the coil bobbin has a structure in which the winding sections that are to be wound by the windings are disposed adjacent to each other in the axial direction, and the curled case is welded to external peripheral sections of the yokes that are made of metal and disposed between the winding sections. The opening section of the curled case may preferably open at an opening arc angle defined by one third of the entire periphery of a circle or less (i.e., 120 degrees or less). As a result, the opening section is narrowed to improve formation of magnetic circuits, and the magnetic circuits are formed more effectively as the curled case is welded to the yokes, and therefore the motor characteristics can be improved.
In accordance with another embodiment of the present invention, a motor comprises a stator and a rotor disposed opposite to the stator, the rotor having a rotor shaft that protrudes from at least one end of the stator and is supported by a frame that is affixed to one end face of the stator provided in the axial direction of the stator. The frame has a fixing surface to be affixed to the stator and the fixing surface of the frame has a passing aperture. In one aspect of the embodiment of the present invention, a cylindrical sleeve section for passing the rotor shaft is provided at an edge of the aperture formed in the stator, and the cylindrical sleeve section is inserted in the passing aperture of the frame. In another aspect of the embodiment of the present invention, the cylindrical sleeve section is formed from a material that has a lower hardness than that of the rotor shaft.
As a result, when the rotor is placed in the stator, the rotor shaft can be prevented from contacting the passing aperture of the frame. Also, even when the rotor shaft contacts the cylindrical sleeve section that extends in the passing aperture of the frame, the rotor central shaft is not damaged because the cylindrical sleeve section is formed from a material having a lower hardness than that of the rotor shaft.
Furthermore, in accordance with another embodiment of the present invention, a motor comprises a stator and a rotor disposed opposite to the stator, wherein the rotor has a metal rotor shaft that protrudes from at least one end of the stator and is supported by a metal frame that is affixed to one end face of the stator provided in the axial direction of the stator.
In one aspect of the invention, the stator has a coil bobbin composed of a resin member and equipped with an aperture section disposed opposite to an external periphery of the rotor, and a yoke having pole teeth disposed opposite to the rotor. The yoke is integrally assembled with the coil bobbin by an insert forming method. The metal frame has a passing aperture that is disposed in a manner to overlap the aperture section of the coil bobbin for passing the rotary shaft. A cylindrical sleeve section that is formed integrally with the coil bobbin by a resin member is inserted in the passing aperture. The cylindrical sleeve section is provided at a peripheral edge of the aperture section of the coil bobbin.
As a result, when the rotor is placed in the stator, the metal rotor shaft can be prevented from contacting the passing aperture of the metal frame. Although there may be a possibility that the rotor shaft may contact the cylindrical sleeve section that extends in the passing aperture of the frame, the rotor central shaft is not damaged because the cylindrical sleeve section provided at the edge of the aperture section of the coil bobbin is formed integrally with the coil bobbin with a resin member.
In the embodiment described above, the measurement of the cylindrical sleeve section in the axial direction may be the same or greater than the measurement of the passing aperture in the axial direction. As a result, the internal peripheral surface of the passing aperture can be completely covered by the cylindrical sleeve section. Moreover, when the rotor is disposed in the stator, the metal rotor shaft can be more thoroughly prevented from contacting the passing aperture of the metal frame.
Also, in the embodiment described above, a convex section may be provided on the external surface of the cylindrical sleeve section, such that the convex section serves as a positioning section to be used when the frame is affixed to the stator. As a result, the frame and the stator can be affixed to each other with a high positional accuracy without having to provide a special positioning section on the end face of the stator.